#include<fstream.h>
int fact ( int n)
{long i,nr2=0,nr5=0,x;
for(i=1;i<=n;i++)
	{x=i;
	while(x%2==0)
		{nr2++;
		x=x/2;}
	while(x%5==0)
		{nr5++;
		x=x/5;}
	}
if(nr5>nr2)
	return nr2;
else
	return nr5;
}
int b(int n, int p)
{if(p==fact(n))
	return n;
else
	if(p>fact(n))
		return b(n+1,p);
	else
		return -1;
}
int main()
{int p;
ifstream fcin("fact.in");
ofstream fcout("fact.out");
fcin>>p;
fcout<<b(1,p);
return 0;
}